Read the following sentence: My ultimate goal as a swimmer is to compete at the national level.

Which of the following correctly describes the verbal and its function in this sentence?

a
To compete is an infinitive doing the job of a noun.

b
To compete is a gerund acting as a noun.

c
To compete is an infinitive doing the work of an adjective.

d
To compete is an infinitive doing the work of an adverb.